The PCI core has historically not allowed drivers to opt in to async
probing: Even though drivers may set "PROBE_PREFER_ASYNCHRONOUS", initial
probing always happens synchronously. That's because the PCI core uses
device_attach() instead of device_initial_probe().
Should a driver return -EPROBE_DEFER on initial probe, reprobing later on
does honor the PROBE_PREFER_ASYNCHRONOUS setting, which is inconsistent.
The choice of device_attach() is likely not deliberate: It was introduced
in 2013 with commit 58d9a38f6fac ("PCI: Skip attaching driver in
device_add()"), but asynchronous probing was added two years later with
commit 765230b5f084 ("driver-core: add asynchronous probing support for
drivers").
According to the kernel-doc of "enum probe_type", "the end goal is to
switch the kernel to use asynchronous probing by default". To this end,
use device_initial_probe() to allow asynchronous probing. The function
returns void, making the return value check unnecessary.
Initial PCI probing often takes on the order of seconds even on laptops,
so this may speed up booting significantly.
Curiously, a small number of PCI drivers already opt in to asynchronous
probing. Their maintainters (who are all cc'ed) should watch out for
issues, now that asynchronous probing is not just allowed for deferred
probing, but also initial probing:
hl_pci_driver drivers/accel/habanalabs/common/habanalabs_drv.c
cxl_pci_driver drivers/cxl/pci.c
quicki2c_driver drivers/hid/intel-thc-hid/intel-quicki2c/pci-quicki2c.c
quickspi_driver drivers/hid/intel-thc-hid/intel-quickspi/pci-quickspi.c
i801_driver drivers/i2c/busses/i2c-i801.c
mei_me_driver drivers/misc/mei/pci-me.c
mei_vsc_drv drivers/misc/mei/platform-vsc.c
sdhci_driver drivers/mmc/host/sdhci-pci-core.c
nvme_driver drivers/nvme/host/pci.c
ehci_pci_driver drivers/usb/host/ehci-pci.c
hvfb_pci_stub_driver drivers/video/fbdev/hyperv_fb.c
All other driver maintainers may test asynchronous probing by specifying
the command line parameter "driver_async_probe=drv_name1,drv_name2,...",
and on success setting "probe_type = PROBE_PREFER_ASYNCHRONOUS" in the
pci_driver struct.
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
---
drivers/pci/bus.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 69048869ef1c..b77fd30bbfd9 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -341,7 +341,6 @@ void pci_bus_add_device(struct pci_dev *dev)
{
struct device_node *dn = dev->dev.of_node;
struct platform_device *pdev;
- int retval;
/*
* Can not put in pci_device_add yet because resources
@@ -372,9 +371,7 @@ void pci_bus_add_device(struct pci_dev *dev)
if (!dn || of_device_is_available(dn))
pci_dev_allow_binding(dev);
- retval = device_attach(&dev->dev);
- if (retval < 0 && retval != -EPROBE_DEFER)
- pci_warn(dev, "device attach failed (%d)\n", retval);
+ device_initial_probe(&dev->dev);
pci_dev_assign_added(dev);
}
--
2.47.2
